A project in the mangrove swamps near the mouth of the Amazon is being showcased at the Johannesburg world development summit as a model of sustainable harvesting.

Local men attack palm trees with machetes to obtain the tender hearts hugely popular as a salad vegetable in Brazil.

The food has played a major part in the destruction of forests in the south of the country.

The crop depends on a healthy forest to make it productive

That is because the usual method of harvesting the hearts at the top of the trunk kills off the entire tree. But here they are doing things differently.

The palm species growing in the Amazon, known as acai, has several stems all of different ages, which can be cut in rotation so that a single plant can produce food for decades - if it is managed properly.

And regular cropping of the stems increases the yield of the dark purple acai fruit, rich in anti-oxidants and other nutrients, which has become a favourite health drink in the beach bars of Rio de Janeiro.

Migration stemmed

The project on the remote island of Marajo is run by a company called Muana Alimentos - its chief executive Georges Schnyder says the crop depends on a healthy forest to make it productive.

"This species needs the organic material which comes from the other trees, and the tides, to fertilise it. So the acai protects the forest, and the forest protects the acai," says Mr Schnyder.

The regular income and employment provided by this business has helped stem the migration of people from this region to the state capital of Belem, seven hours' boat ride away through pirate-infested waters.

There, many fall into a desperate lifestyle of begging or prostitution.

Showcase

Helios Rodrigues, 21, now sees a future for himself and his family in his forest community, thanks to the methods being used to cut the palms.

It's absolutely for profit, period... The type of customers who are speaking to us are global players, big food companies

John Forgach

"In the old days we used to take the palm out of the forest without putting things back.

"By doing things this way we can get heart of palm and the fruit throughout the year, and for ever. It's taught us to be self-sufficient, and with that we can survive here."

The project is being seen as an example of how sustainable harvesting of the forest's products can provide a more secure income than activities which destroy it - but only if such businesses can find investment to enter the global food market.

In the case of Muana, an investment of $1.5m has come from an equity fund called Terra Capita, which specialises in putting capital into companies which can demonstrate that they are acting responsibly to protect the environment and local communities.

Drop in the ocean

Speaking from his headquarters in a sleek skyscraper in Sao Paulo, the head of that fund, John Forgach says the attraction of the company is not so much that it is green, but that it can offer a good return without the risks attached to the unscrupulous businesses which dominate the heart of palm market.

Stems are now cut in rotation

"It's absolutely for profit, period. The type of customers who are speaking to us are global players, big food companies," says Mr Forgach.

"These big corporations are very interested in coming into this market, and what they are concerned about is bottom line.

"But they understand that to achieve a bottom line they have to be sustainable, they have to be clean, and they have to be honest."

The investment has helped Muana to get international organic certification for their produce, and the project is the first non-timber business to get approval from the Forest Stewardship Council, the body which guarantees that trees are not being depleted faster than they can be replaced.

This should help the business earn valuable export opportunities and offer further protection to the area.

Of course, sustainable projects like Muana are still a drop in the ocean compared with the millions being made through logging or farming in cleared areas.

But it suggests that the market can play an important role in protecting areas like the Amazon - so long as hard-headed investors can be convinced that the value of an intact forest is greater in the long term than the profits to be made from destroying it.